HY-GRO '92 is a project currently carried out by the Ocean Mapping Group at the University of New Brunswick. One of the purposes of this project is the investigation of the relationship between acoustic mapping data and the actual ocean seabed bathymetry. In order to facilitate the comparison, ground truthing information (Digital Elevation Model) has been collected using stereo aerial photography of tidal areas at low tide. The required DEM accuracy is in the magnitude of a few centimeters. A reasonable photoscale for providing the required DEM accuracy would be 1:3750. With a focal length of 80 mm the flying height has to be 300 m. In that case the ground coverage of the 57 X 57 mm2 image format is 214 X 214 m2. It is clear that for large areas of interest (in our case: 2.5 X 2.5 km2) while maintaining the necessary overlap (60%) and sidelap (30%), the number of photographs and control points becomes unreasonably high, thus making the use of the small format camera not attractive anymore. The above encountered problem was solved with the acquisition of the original images in a four times smaller scale (1:15,000, flying height 1200 m, ground coverage 857 X 857 m2). Using a quality enlarger, the original images are enlarged by the same factor, so that the final image product is at the desired scale. The enlargement introduces effects of lens distortions and film deformations but they are again taken care of by the self calibrating bundle adjustment.